1. Field of the Invention
This invention relates to an electronic imaging apparatus using an imaging device having very fine pitch of a picture element.
2. Description of the Related Art
In recent electronic imaging apparatus including digital camera, the increase in the number of picture element in a high-class type and the miniaturization of imaging element in a popular type are remarkable. A common point in these two tendencies is that the pitch of the picture element of the imaging element in the both types tends to become much finer. In a conventional electronic imaging apparatus, the apparatus having an optical performance sufficient to the Nyquist frequency decided from the pitch of the picture element of an imaging device as an imaging optical system has been used. However, if the pitch of the picture element is fine, the Nyquist frequency will become high frequency, and the optical performance required for the optical system will also become very high.
In order to cope with such aspects, in the imaging optical system, it is required that the compensation level of geometric aberration is improved and that a manufacture error does not affect performance degradation, etc. Moreover, by a pitch of the picture element becoming smaller, the point spread function by the imaging optical system spreads relatively. And the level of the influence of quality of image degradation by so-called diffraction shade cannot be disregarded.
Moreover, in a conventional electronic imaging apparatus, an optical low-pass filter is inserted in optical path in order to prevent from distortion by light return and to eliminate intentionally contrast having frequency component more than Nyquist frequency. However, an optical low-pass filter is expensive and when it is built in an optical path of an electronic imaging apparatus, the volume or size of apparatus will increase. Moreover, there is a problem of reducing the contrast in low spatial frequency, and degrading imaging performance that an imaging optical system has originally.
For example, an imaging apparatus described in Japanese Patent Preliminary Publication No. 2000-244799 is conventionally proposed as an electronic imaging apparatus by which a high grade picture is obtained using an imaging element having very fine pitch of a picture element, without using an optical low-pass filter